But as the insects search for somewhere to dive in, the nerves in hairs also increase the chances of them being felt on the skin and swatted away.

Researchers studied 29 brave volunteers who had one arm shaved before hungry bed bugs were placed on their skin

The results of the experiment showed that people with more hair - both longer hairs and fine, almost invisible 'vellus' hairs - were more protected.

Hair covering the arms extended each insect’s search for an ideal feeding ground, and increased the likelihood of it being detected.

Because of this, bed bugs and other parasites including mosquitoes, midges, ticks and leeches prefer relatively hairless areas such as the wrists and ankles, the scientists claim.

Study leader Professor Michael Siva-Jothy, from the University of Sheffield’s Department of Animal and Plant Sciences, said: 'Our findings show that more body hairs mean better detection of parasites.

'The hairs have nerves attached to them and provide us with the ability to detect displacement. By forming a barrier and providing detection, these hairs prolong search time and make detection more likely because the bug has to spend more time clambering over them.

'The results have implications for understanding why we look the way we do, what selective forces might have driven us to look the way we do, and may even provide insight for better understanding of how to reduce biting insects’ impact on humans.'

The findings may explain why humans have retained a body-covering of fine hair.

'Our proposal is that we retain the fine covering because it aids detection and if we lost all hair, even the relatively invisible fine hair, our detection ability goes right down,' said Prof Siva-Jothy.

The research is published today in the Royal Society journal Biology Letters. Prof Siva-Jothy said it would be wrong to assume women will always be bitten more often than hairier men.

He pointed out: 'Men have more body hair than women which is caused by the action of testosterone at puberty. This does not necessarily mean that women are more likely to be bitten.

'Blood-sucking insects are likely to have been selected to prefer to bite hosts in relatively hairless areas.”

The Sheffield scientists are investigating the biology, reproduction and immunity of blood-sucking insects.

Their aim is to find more effective ways of controlling parasitic insects and the diseases they spread.